Question

the figure above represents a phylogenetic tree of birds and their closest relatives. which group of organisms represents the outgroup in this clade?

lizards and snakes
crocodilians
ornithischian dinosaurs
birds

Explanation:

Identify the ingroup and outgroup

Using the Cladogram Outgroups and Phylogenetic Trees knowledge points

The phylogenetic tree shows evolutionary relationships among several reptile lineages. The prompt asks for the outgroup relative to the clade containing crocodilians, dinosaurs, and birds.

The node labeled "Common ancestor of crocodilians, dinosaurs, and birds" defines the ingroup clade (Archosauria). The lineage that branches off prior to this shared common ancestor is the "Lizards and snakes" group (Lepidosauria), which serves as the outgroup.

Evaluate the multiple-choice options

Using the Cladogram Outgroups knowledge point

• lizards and snakes: Correct. This group diverged before the common ancestor of the archosaur clade.
• crocodilians: Incorrect. They belong to the ingroup.
• ornithischian dinosaurs (labeled as "Other dinosaurs" in the tree): Incorrect. They belong to the ingroup.
• birds: Incorrect. They belong to the ingroup.

Answer:

• (A) lizards and snakes (Correct answer)
• (B) crocodilians
• (C) ornithischian dinosaurs
• (D) birds